The present invention relates to a system and method for performing a volume based three-dimensional virtual examination using planned and guided navigation techniques. One such application is performing a virtual endoscopy.
Colon cancer continues to be a major cause of death throughout the world. Early detection of cancerous growths, which in the human colon initially manifest themselves as polyps, can greatly improve a patient""s chance of recovery. Presently, there are two conventional ways of detecting polyps or other masses in the colon of a patient. The first method is a colonoscopy procedure, which uses a flexible fiber-optic tube called a colonoscope to visually examine the colon by way of physical rectal entry with the scope. The doctor can manipulate the tube to search for any abnormal growths in the colon. The colonoscopy, although reliable, is both relatively costly in money and time, and is an invasive, uncomfortable painful procedure for the patient.
The second detection technique is the use of a barium enema and two-dimensional X-ray imaging of the colon. The barium enema is used to coat the colon with barium, and a two-dimensional X-ray image is taken to capture an image of the colon. However, barium enemas may not always provide a view of the entire colon, require extensive pretreatment and patient manipulation, is often operator-dependent when performing the operation, exposes the patient to excessive radiation and can be less sensitive than a colonoscopy. Due to deficiencies in the conventional practices described above, a more reliable, less intrusive and less expensive way to check the colon for polyps is desirable. A method to examine other human organs, such as the lungs, for masses in a reliable, cost effective way and with less patient discomfort is also desirable.
Two-dimensional (xe2x80x9c2Dxe2x80x9d) visualization of human organs employing currently available medical imaging devices, such as computed tomography and MRI (magnetic resonance imaging), has been widely used for patient diagnosis. Three-dimensional images can be formed by stacking and interpolating between two-dimensional pictures produced from the scanning machines. Imaging an organ and visualizing its volume in three-dimensional space would be beneficial due to its lack of physical intrusion and the ease of data manipulation. However, the exploration of the three-dimensional volume image must be properly performed in order to fully exploit the advantages of virtually viewing an organ from the inside.
When viewing the three dimensional (xe2x80x9c3Dxe2x80x9d) volume virtual image of an environment, a functional model must be used to explore the virtual space. One possible model is a virtual camera which can be used as a point of reference for the viewer to explore the virtual space. Camera control in the context of navigation within a general 3D virtual environment has been previously studied. There are two conventional types of camera control offered for navigation of virtual space. The first gives the operator full control of the camera which allows the operator to manipulate the camera in different positions and orientations to achieve the view desired. The operator will in effect pilot the camera. This allows the operator to explore a particular section of interest while ignoring other sections. However, complete control of a camera in a large domain would be tedious and tiring, and an operator might not view all the important features between the start and finishing point of the exploration. The camera could also easily get xe2x80x9clostxe2x80x9d in remote areas or be xe2x80x9ccrashedxe2x80x9d into one of the walls by an inattentive operator or by numerous unexpected obstacles.
The second technique of camera control is a planned navigation method, which assigns the camera a predetermined path to take and which cannot be changed by the operator. This is akin to having an engaged xe2x80x9cautopilotxe2x80x9d. This allows the operator to concentrate on the virtual space being viewed, and not have to worry about steering into walls of the environment being examined. However, this second technique does not give the viewer the flexibility to alter the course or investigate an interesting area viewed along the flight path.
It would be desirable to use a combination of the two navigation techniques described above to realize the advantages of both techniques while minimizing their respective drawbacks. It would be desirable to apply a flexible navigation technique to the examination of human or animal organs which are represented in virtual 3D space in order to perform a non-intrusive painless thorough examination. The desired navigation technique would further allow for a complete examination of a virtual organ in 3D space by an operator allowing flexibility while ensuring a smooth path and complete examination through and around the organ. It would be additionally desirable to be able to display the exploration of the organ in a real time setting by using a technique which minimizes the computations necessary for viewing the organ. The desired technique should also be equally applicable to exploring any virtual object.
The invention generates a three-dimensional visualization image of an object such as a human organ using volume visualization techniques and explores the virtual image using a guided navigation system which allows the operator to travel along a predefined flight path and to adjust both the position and viewing angle to a particular portion of interest in the image away from the predefined path in order to identify polyps, cysts or other abnormal features in the organ.
The inventive technique for three-dimensional virtual examination of an object includes producing a discrete representation of the object in volume elements, defining the portion of the object which is to be examined, performing a navigation operation in the virtual object and displaying the virtual object in real time during the navigation.
The inventive technique for a three-dimensional virtual examination as applied to an organ of a patient includes preparing the organ for scanning, if necessary, scanning the organ and converting the data into volume elements, defining the portion of the organ which is to be examined, performing a guided navigation operation in the virtual organ and displaying the virtual organ in real time during the guided navigation.
In performing virtual examination, it is often desirable to view a particular material type while removing other material types from the image. To perform such an operation, a method for electronically cleansing an image can be performed by converting the image data to a plurality of volume elements with each volume element having an intensity value. Next, a classifying operation is performed to classify the volume elements into a plurality of clusters in accordance with the intensity values. Once classified, at least one cluster of volume elements can then be removed from the image data.
The classifying operation can be performed by evaluating a plurality of volume elements of the image data with respect to a plurality of neighboring volume elements to determine a neighborhood similarity value for the volume element.
The clusters can be further classified by applying a mixture probability function to the clusters to classify voxels whose intensity value results from inclusion of more than one material type.
An alternative classifying operation includes the steps of performing feature vector analysis on at least one of the clusters which include image data for a material of interest followed by performing high level feature extraction to remove volume elements from the image which are not substantially indicative of the material of interest.
The method according method for electronically cleansing an image is well suited for applications where the image data represents a region of the human body including at least a portion of the colon and the material of interest is tissue of a colon. In colon imaging applications, the removing operation can remove volume elements representing intracolonic fluid, residual stool within the colon, bone, and non-colonic tissue.
It is an object of the invention to use a system and method to perform a relatively painless, inexpensive and non-intrusive in vivo examination of an organ where the actual analysis of the scanned colon can be possibly performed without the patient present. The colon can be scanned and visualized in real-time or the stored data can be visualized at a later time.
It is another object of the invention to generate 3D volume representations of an object, such as an organ, where regions of the object can be peeled back layer by layer in order to provide sub-surface analysis of a region of the imaged object. A surface of an object (such as an organ) can be rendered transparent or translucent in order to view further objects within or behind the object wall. The object can also be sliced in order to examine a particular cross-section of the object.
It is another object of the invention to provide a system and method of guided navigation through a 3D volume representation of an object, such as an organ, using potential fields.
It is a further object of the invention to calculate the center-line of an object, such as an organ, for a virtual fly-through using a peel-layer technique as described herein.
It is still a further object of the invention to use a modified Z buffer technique to minimize the number of computations required for generating the viewing screen.
It is another object of the invention to assign opacity coefficients to each volume element in the representation in order to make particular volume elements transparent or translucent to varying degrees in order to customize the visualization of the portion of the object being viewed. A section of the object can also be composited using the opacity coefficients.